Carbon-carbon composites are often formed by laying up woven or nonwoven fabrics or by molding a mixture of loose fiber segments. The fibers in the fabrics and fiber segments are typically derived from pitch, cotton, polyacrylonitrile, or rayon. They are ordinarily joined together by a fusible binder, such as a phenolic resin or furan resin or by needling. The resulting fiber/resin preform is carbonized. That is, the preform is heated to a temperature that drives hydrogen, oxygen, and other elements out of the carbon-skeleton fibers and binders, leaving residual carbon. To reduce voids and increase the density of the carbon-carbon composite preforms, the carbon-carbon composite is infiltrated, e.g. with a phenolic resin or other carbonizable matrix material using a vacuum followed by pressure, and the infiltrated material is then carbonized by heating. Densification is also accomplished by chemical vapor infiltration (CVI) or chemical vapor deposition (CVD). One or more of these chemical infiltration processes is generally repeated three to five times or more before the desired density (at least 1.7 g/cc for friction applications) is achieved. The lengths of time necessary for this heating and infiltration processing is significant. For instance, it may take up to five months to form a carbon-carbon composite brake disc, depending on the number of densification steps used in its preparation.
U.S. Pat. No. 5,061,414 describes a typical method of making a carbon-carbon composite. Mesophase pitch-derived carbon fibers are woven into a cloth, and layers of the cloth are covered with petroleum or coal tar pitch and pressed at a temperature above the softening point of the pitch to form a laminated composite. The composite is restrained in a suitable fixture and heated to carbonize the pitch binder. The carbonized composite is then impregnated several times with pitch by covering the composite with hot pitch under pressure. The composites are heat-treated between each impregnation step to crack up the infiltrated carbon and allow additional pitch to enter the microstructure during the next impregnation cycle. The impregnated composites are then given a final heat treatment in the range 2500-3000° C. to fully graphitize the fibers and the matrix carbon. The composites are then infiltrated with pyrolytic carbon by CVD processing at 1000-1300° C. for 150 hours.
US 2004/0105969 A1 discloses that a mixture of carbon-containing fibers and a suitable matrix material is compressed while resistively heating the mixture to form a carbonized composite material having a density of at least 1.30 g/cc. This composite is formed in less than 10 minutes, which is said to be significantly shorter than conventional processes taking several days and achieving lower density material. Following impregnation of this composite, final densities of 1.6-1.8 g/cc are said to be readily achievable with one or two infiltration cycles, using a pitch or other carbonaceous material to fill voids in the composite, and rebaking.
U.S. Pat. No. 6,537,470 B1 describes break-through technology in which a resin transfer molding process is used to rapidly fill fibrous preforms with high viscosity resin or pitch.
Typically, pitch infiltration of carbon fiber preforms takes 8-10 hours and requires a vacuum pump. In such processing, the carbon fiber preforms are normally heated under vacuum.